Gangrene is divided into dry gangrene, wet gangrene and gas gangrene. Gangrene is more common in limbs, which occurs when the artery is occluded and the venous return is unobstructed. It is black due to ischemia and dryness, and has obvious inflammatory boundary with normal tissue. Because it is on the body surface, the odor and systemic poisoning symptoms are mild. Wet gangrene is more common in organs communicating with the outside world, but water is not easy to evaporate. Occurred in arterial occlusion, venous reflux obstruction, congestion and edema, local tissue swelling, moist and dark green. Because of the diffuse inflammation, there is no obvious boundary with normal tissues, and the stench is serious, with symptoms of systemic poisoning. Common gangrenous appendicitis and intestinal gangrene. Gas gangrene is a special type of wet gangrene, which is common in open wounds that go deep into muscles and is infected by anaerobic bacteria such as Clostridium perfringens. The necrotic tissue is honeycomb-shaped and feels distorted when pressed. Systemic poisoning has serious symptoms, rapid development and serious consequences.